1. Field of the Invention
The present invention relates generally to a device which bends a sheet metal workpiece, and to a system for changing the die on that device, and, more particularly, to a device which maintains a sheet metal workpiece in a horizontal plane so that it is capable of being conveyed, for example, in a horizontal line, and which bends the edge of that workpiece in, for example, an L-shape, and to a die exchange system for such a bending machine which is capable of quickly changing a die made up of separate sections assembled to a length conforming to the width of the workpiece.
2. Description of the Prior Art
As an example of a device which holds a workpiece horizontally and bends an edge of that workpiece into an L-shape, a tangent bender, for example, is commonly known. The tangent bender is provided with a bottom die which supports the workpiece from the bottom, and a top die freely movable in the vertical direction which presses the workpiece from the top against the bottom die. It is also provided with a freely rotatable bend-beam which bends the edge of the workpiece upward, while that workpiece is secured by the application of pressure between the bottom die and top die. Generally, the bend-beam on the tangent bender is supported in a freely rotatable manner at both ends only, so when the workpiece is being bent there is a tendency for an inflection to occur near the center of the bend-beam from the drag of the workpiece, making it difficult to carry out the bending operation with a satisfactory degree of precision. Accordingly, to suppress this inflection, the width of the bend-beam is made larger near its center.
As outlined above, because the bend beam on a conventional tangent bender is comparatively wide near its center, if the workpiece is conveyed, when the tangent bender is positioned in the process line where the bending operation is carried out, the wide part of the bend-beam hinder in positioning on the transportation roller. This is not suitable for a process line where the object is a workpiece of comparatively small width. Also, in a process where one edge of a plate-shaped workpiece and then the other edge is to be bent continuously, when a pair of tandem benders are positioned opposingly with the process line in the center, it is necessary to separate the bender beams on these tandem benders a comparatively large distance to prevent interference, which is not a desirable situation.
In addition, the top die in a tangent bender is installed on the bottom of a ram which is capable of moving freely in the vertical direction, which is intended to conform to sheet metal workpieces of diverse widths, and which, generally, is formed of a divided die assembled in freely diverse lengths. Specifically, this top die is formed of a plurality of divided leaves appropriately combined in diverse lengths. In changing this top die to conform to the width of the workpiece, a die-changing robot, for example, is used, and each split leaf can be mounted or dismounted on the ram. Accordingly, a considerable amount of time is used in dismounting and mounting this top die on the ram when making a change, making it difficult to improve operating efficiencly.